Switches to which the present invention is applicable include electromagnetic contactors and wiring interrupters.
First, one example of a conventional electromagnetic contactor will be described with reference to FIG. 1. In FIG. 1, (1) is a mount bed molded from a plastic material, (2) is a stationary iron core of silicon steel laminations disposed on the mount bed, (3) is a movable core disposed in a facing-relationship with the stationary core (2) and made of silicon steel laminations, (4) is an operating coil for providing a driving force which attracts the movable core (3) to the stationary core (2) against a trip spring (not shown), and (5) is a cross bar made of a plastic material and having a rectangular window, the bottom end of which has attached thereto the movable core (3). (6) is a movable contact inserted within the rectangular window of the cross bar (5) and held under pressure by a compression spring (7), (6A) is a movable contact (6) element disposed on the movable contact, (8) is a stationary contact facingly disposed with respect to the movable contact (6) for conducting a current, (8A) is a stationary contact element disposed on the stationary contact (8), and (8C) is a terminal portion for the stationary contact (8). (9) is a terminal screw for connecting the electromagnetic contactor main body to an external circuit, (10) is a base for mounting the stationary contact (8), and (11) is a cover for covering the upper portion of the electromagnetic contactor. The manner of mounting of the stationary contact (8) and the stationary contact element (8A) is shown in the enlarged views of FIGS. 2(a) and 2(b).
Since the conventional electromagnetic contactor has the above-described structure, when the operating coil (4) is de-energized, the unillustrated trip spring causes the movable core (3) to separate from the stationary core (2) and the cross bar (5) occupies the position shown in FIG. 1, whereby the movable contact element (6A) and the stationary contact element (8A) are separated to generate an electric arc (12), the arc (12) being extinguished at the zero current point to interrupt the electric current.
In the conventional electromagnetic contactor, as shown in FIG. 3, the arc (12) is subjected to a driving force F.sub.2 due to a magnetic field formed by a current I flowing through the movable contact (6) and a driving force F.sub.1 due to a magnetic field formed by a current I flowing through the stationary contact (8). Since the driving forces F.sub.1 and F.sub.2 are substantially equal in intensity and opposite in direction, the arc (12) stays on the movable contact element (6A) and the stationary contact element (8A). Thus, since the arc (12) is not driven, the legs of the arc do not move outside of the contact elements thereby resulting in large disadvantage that the wear of the contact elements occurs.